The present invention relates to a therapeutic agent for spinal canal stenosis, which contains a specific pyridazinone compound or its pharmacologically acceptable salt.
The pyridazinone compound and its salt in the present invention are known to have a superior platelet aggregation inhibitory action, a cardiotonic action, a vasodilating action, an anti-SRS-A (Slow Reacting Substances of Anaphylaxis) action, a thromboxane A2 synthase inhibitory action and the like (JP-B-7-107055, JP-A-7-285869), and are expected as an anti-platelet agent and the like.
However, there are no reports on what effect the pyridazinone compound has on spinal canal stenosis.
The spinal canal stenosis is caused by a pressure on the cauda equina nerve from the stenosed spinal canal due to underdevelopment of spinal canal, spondylosis deformans, degenerative intervertebral discs, degenerative spondylolisthesis, ossification of the yellow ligaments and the like, and is characterized by intermittent claudication. The symptoms of the disease generally surface after middle age when retroplasia begins.
Particularly, lumbar spinal canal stenosis, in which the cauda equina nerve and nerve root in the lumbar portion are compressed, causes lumbago, melosalgia and intermittent claudication.
The cervical spinal canal stenosis generally appears as cervical spondylosis, and shows the symptoms of numbness of fingers, paralysis, spastic walking, paraplegia and the like.
While there are various therapeutics for spinal canal stenosis, including the drug therapy as one of the established therapeutics, a much superior drug therapy is awaited.
It is therefore an object of the present invention to provide a superior therapeutic agent for spinal canal stenosis.
The present inventors have made various studies and found that the pyridazinone compound of the following formula (I) and its pharmacologically acceptable salt have a superior effect on spinal canal stenosis, which resulted in the completion of the present invention.
Accordingly, the present invention provides a therapeutic agent for spinal canal stenosis, which contains a pyridazinone compound of the formula (I) 
wherein R1, R2 and R3 are each independently a hydrogen atom or a lower alkyl, X is a halogen atom, a cyano or a hydrogen atom, Y is a halogen atom, a trifluoromethyl or a hydrogen atom, and A is a C1-C8 alkylene optionally substituted with a hydroxyl, or its pharmacologically acceptable salt.
Preferably, the present invention provides a therapeutic agent for spinal canal stenosis, which contains a pyridazinone compound of the formula (I) wherein R1 and R2 are each hydrogen atom, R3 is hydrogen atom or C1-C4 alkyl, X is halogen atom, Y is halogen atom or hydrogen atom, and A is C1-C5 alkylene optionally substituted with hydroxyl, or its pharmacologically acceptable salt.
A particularly preferable example of the pyridazinone compound of the formula (I) is 4-bromo-6-[3-(4-chlorophenyl)propoxy]-5-(3-pyridylmethylamino)-3(2H)-pyridazinone.